This invention relates to a mobile telephone system, and more particularly to a process of zone registration of a mobile radio station in the system.
In a service area for a mobile radio station, there are plural base radio stations, and the mobile radio station is connected to a desired telephone subscriber through one of these base radio stations, a radio channel control unit, and a private exchange equipment(PBX). One radio channel control unit is provided in common in a service area and controls all the base radio stations in the service area. An area where a base radio station connects a mobile radio station in the area to a telephone subscriber is called a service zone or simply a zone of the base radio station.
For smooth operation of originating and receiving calls in this system, the radio channel control unit which controls the entire system, must remember the identifications of all the mobile radio stations in connection with the identifications the service zones to which they belong. And each mobile radio station must remember the identification of the zone of the station and must originate a call to the base radio station in the zone.
Thus, zone registration of mobile radio stations is carried out in this system, and there have been two different modes of zone registration in systems heretofore known. One mode of zone registration is carried out manually at an initialization, and the other mode of zone registration is carried out automatically and periodically.
At an initialization, a mobile radio station transmits a request signal of registration including the identification signal of the station on a radio channel. This request signal is received at plural base radio stations in the service area. Each base radio station which receives this request signal measures the field intensity of the request signal and reports the measured field intensity to the radio channel control unit through a cable laid between the base radio station and the radio channel control unit. The radio channel control unit compares the values of the field intensities measured at the base radio stations and chooses a service zone having the highest field intensity for the mobile radio station as the zone of the mobile radio station. The radio channel control unit registers this decision in a zone register, and notifies this decision to a base radio station whose service zone is registered as the zone of the mobile radio station. The base radio station notified by the radio channel control unit communicates the decision to the mobile radio station, where this decision is registered in a zone register of the mobile radio station.
In an automatic registration mode, all the base radio stations, controlled by the radio channel control unit, broadcast, periodically and in time division, a zone signal including the identification signal and followed by a battery saving signal.
For the sake of saving battery consumption in a mobile radio station, the receiver of the mobile radio station is power-supplied only intermittently in a standby mode. When a signal is received in this intermittent receiving mode, the receiver is continuously power-supplied and receives the transmitted message. When the battery saving signal is received at the end of the message, the receiver returns to the standby mode.
A mobile radio station receives the zone signals from all the base radio stations in a time sharing sequence, and measures the field intensity of these zone signals. If the zone signal which have the highest field intensity is not from a base radio station which is registered in the zone register of the mobile radio station, the mobile radio station automatically transmits a request signal to the base radio station having the highest field intensity. The base radio station which receives this request signal from the mobile radio station reports the signal to the radio channel control unit, and the contents of the zone register in the radio channel control unit is revised in accordance with the report.
As described in the foregoing paragraphs there have been two modes of zone registration, and in an automatic mode, each mobile radio station must be equipped with a field intensity meter. For the two modes of operation, two control programs are required. This makes the control program and control itself complex. The field intensity meter is made up of a simple circuit in a radio receiver, but it makes the total cost of the system higher to provide field intensity meters and automatic control circuits related to the field intensity meters for all the mobile radio stations.